One problem with conventional high pressure pneumatic drilling hammers, is that they permit too much compressed air to pass through the working parts, and thus do not make fully economical use of the compressed air.
This problem arises because the passages used to convey fluid to the chambers for reciprocating the piston, are lengthy, and usually comprise cutouts within the internal diameter of the sleeve. The chambers are filled and emptied with every stroke of the piston, whereas this is not strictly necessary for the functioning of such a hammer drill.